Acute limb ischemia

Acute limb ischemia (ALI) is a vascular emergency in which the arterial blood supply to one or more extremities is critically reduced. Arterial thrombosis and cardiac emboli are responsible for the majority of cases. The typical signs and symptoms of ALI include pain, pallor, pulselessness, poikilothermia, paralysis, and paresthesia of the limb distal to the site of vascular occlusion (the 6 Ps). Diagnosis relies on examination and arterial Doppler studies. Clinical findings in combination with Doppler studies are then used to categorize the limb as viable, threatened, or nonviable. Further imaging studies, e.g., digital subtraction angiography, should only be performed if they do not result in treatment delays. Management of viable and threatened limb ischemia begins with intravenous heparin followed by revascularization. Irreversible limb ischemia will inevitably progress to gangrene and requires amputation of the nonviable parts of the limb. Whether long-term anticoagulation and/or further diagnostic studies are required depends on the suspected etiology (e.g., echocardiography in suspected left atrial thrombus formation).

• Arterial occlusion ^[1][2][3]
  • Thrombosis
    • Peripheral arterial disease
    • Stent or graft thrombosis
    • Aneurysmal thrombosis (most commonly popliteal aneurysms)
    • Vasculitis, thrombophilia (rare)
  • Embolism
    • Cardiac emboli
      • Atrial fibrillation (most common)
      • Myocardial infarction
    • Cholesterol embolism (e.g., blue toe syndrome)
    • DVT (paradoxical embolism via a patent foramen ovale)
    • Septic emboli (e.g., from endocarditis)
    • Proximal aneurysms (aortic, popliteal) or atherosclerotic lesions
  • Trauma leading to transsection, dissection, or thrombosis of a vessel
    • Posterior knee dislocations (e.g., popliteal artery thrombosis)
    • Iatrogenic injury at the site of arterial access (e.g., femoral artery thrombosis)
    • Crush injury of a limb
  • Aortic dissection
  • Compartment syndrome
• Arterial vasoconstriction
  • Shock (e.g., sepsis)
  • Vasoactive drugs (e.g., norepinephrine)
  • Raynaud phenomenon
    
• Venous occlusion (phlegmasia cerulea dolens)

References:^[4]

• The lower limb is affected in > 80% of cases.
• Arterial thrombosis: subacute onset; history of claudication pain
• Embolism: acute onset; history of heart disease (e.g., atrial fibrillation)
• The 6 Ps of ALI distal to the site of occlusion
  • Pain
  • Pallor
  • Pulselessness
  • Paralysis
  • Paresthesia
  • Poikilothermia

References:^[4]

Leriche syndrome (aortoiliac occlusive disease)

Occlusion at the level of the aortic bifurcation or bilateral occlusion of the iliac arteries that usually presents with:

• Pain in both legs and the buttocks
• Bilaterally absent femoral, popliteal, and ankle pulses
• Erectile dysfunction
• Shock

Hair tourniquet syndrome

• Definition: : a condition in which a hair or thread becomes wound around an appendage tightly, putting the appendage at risk of ischemic damage
• Epidemiology: usually affects infants
• Pathophysiology: hairs or threads inside socks or under bed sheets can become spontaneously tied round a toe and tighten with the child's movement → venous and lymphatic return is impaired → further obstruction may cause arterial occlusion and ischemic injury
• Clinical features: painful, swollen, reddened appendage with a deep groove proximal to it, in which the constricting fiber may be visible
• Treatment: prompt removal of the constricting hair or fiber, either by means of a hair-dissolving product or a scalpel

Drug-induced vasoconstriction

• Definition: peripheral ischemia due to prolonged treatment with vasopressors (e.g., norepinephrine)
• Pathophysiology: prolonged alpha receptor agonism → vasospasm of distal arterioles and their branches → ischemia and consequent necrosis of most distal extremities
• Clinical features: symmetrical cyanosis, coldness, and necrosis of fingers and/or toes

References:^[5]

The severity of ALI is assessed through physical examination and Doppler studies. Affected limbs can range from viable to nonviable (irreversible ischemia).

References:^[4]

• Tests to confirm the diagnosis and identify the site(s) of occlusion
  • Best initial test: arterial and venous Doppler
    • Diminished or absent Doppler flow signal distal to site of occlusion.
  • Confirmatory test: angiography (DSA, CTA, MRA)
    • Digital subtraction angiography (DSA) is the imaging modality of choice.
    • Should only be performed if delaying treatment for further imaging does not threaten the extremity
• Depending on the suspected etiology, other tests may be indicated (e.g., echocardiography if an arterial embolism is suspected).

References:^[4]

• Acute limb ischemia due to thromboembolism
  • Systemic anticoagulation with an IV heparin bolus followed by continuous infusion unless a contraindication is present
  • Further management depends on the severity of acute limb ischemia.
    • Viable, non-threatened limb
      1. Urgent angiography to localize the site of the occlusion
      2. Revascularization procedure (open or catheter-directed thrombectomy or thrombolysis) within 6–24 hours
    • Threatened limb: emergent revascularization procedure within 6 hours
      • First-line: catheter-directed thrombolysis and/or percutaneous mechanical thromboembolectomy (e.g., balloon catheter embolectomy)
      • Second-line: open thromboembolectomy
    • Non-viable limb: limb amputation
• Acute limb ischemia due to compartment syndrome: fasciotomy (see compartment syndrome)
• Acute limb ischemia due to a dissecting aneurysm: stenting and/or surgical repair

• Permanent nerve damage: sensory loss, muscle weakness, paralysis
• Loss of limb due to irreversible ischemia
• Reperfusion injury (postischemic syndrome)

We list the most important complications. The selection is not exhaustive.